Corona discharge devices are used to treat the surface of various materials such as polyethylene web, by passing the web between a pair of electrodes. Generally, one of the electrodes comprises a grounded treater roll which is used to carry the web through a discharge zone, and a electrode assembly mounted for movement between an operative position spaced from the treater roll and an inoperative position for maintenance or repair. The electrode assembly includes a plurality of electrodes connected to a high voltage source and mounted on a common base with a hollow, ceramic or insulating member associated with each of the electrodes. The electrodes are offset from one another to provide a corona discharge across the entire surface of the web. The corona discharge treatment results in changing the molecular structure of the web so as to increase the wettability of the web which, in turn, makes the surface more amenable to receiving and retaining an applied coating such as, for example, printing ink for printing indicia on the web of a label press or the like.
The corona discharge device or treater has an electrode magazine that is normally removed for periodic cleaning and maintenance of the electrodes. In past designs, the connection between the high voltage source and the electrodes would normally be a high voltage wire joined permanently to the electrodes making it very difficult and extremely dangerous to remove the electrode magazine from the treater.
The corona treater also has mounting plate structure which connects the corona treating equipment to the frame of the label press. A front mounting plate normally supports the treater roll as well as a pair of web guide rolls and an electrode support tube, and provides the necessary alignment to reduce wrinkles and twisting of the web. In the past narrow web designs, the rolls were cantilevered from a single mounting plate or supported to permanently mounted plates at each end of the treater. The cantilevered design would not provide the mechanical strength for the longer treat width system and the two-plate design made installation difficult and more specifically designed for a particular press manufacturer.
The corona treating system further includes a mechanism to thread the web through the treater system and in addition, a method of cleaning the electrode assembly and performing maintenance. In the past, the electrode magazine would normally fasten to the electrode support tube and require the assembly to be rotated away from the treater roll before the magazine could be moved or cleaned. This method is very costly and takes up additional machine space for the pivoting of the electrode assembly.
The corona treater additionally has a mechanism which is used to adjust the gap between the high voltage electrodes and the treater roll. In past systems, this adjustment was normally accomplished with an adjustment device located on each end of the electrode assembly which raises and lowers the electrode depending on how far the adjustment device was turned. This type of adjustment did not provide consistent gap adjustment on both ends of the electrode assembly and requires a gapping gauge to set the proper distance between the electrode and the treater roll.
Accordingly, it is desirable to rectify the shortcomings of prior art constructions by providing a corona treater having a fast and simple, high voltage connection between the electrodes and high voltage source and which can be easily disconnected from the corona treater making removal of the electrode magazine safer and quicker. It is also desirable to provide a corona treater having a mounting plate design with the ability to adjust the frame to the type of press it was being mounted to allowing for a standard machine design for all presses. There is a need for a corona treater having a simple mechanism to support the electrode magazine which can easily slide out partially to allow webbing of the treater roll or can be completely removed for maintenance and cleaning. Likewise, there is a need for a corona treater having a single adjustment device at the front end of the treater system which is easily accessible to the operator. Such a single device when operated will adjust the electrode gap evenly across the treater roll surface and prevent uneven treatment levels due to improper adjustment.